Role of pre-corrosion of Fe⁰ on its efficiency in remediation systems: An electrochemical study

The duration of in-situ generation of iron corrosion products (FeCPs) prior the remediation process (so called "aging" of metallic iron (Fe⁰)), was found as the key parameter affecting the efficiency of Fe⁰ for water remediation. Batch experiments were performed in buffered solutions (pH 4.0, 4.7 and 5.5) and under oxic conditions (presence of dissolved oxygen) using Zn²⁺ as probe contaminant. The time-dependent (0-16 d) concentration changes of aqueous Fe²⁺ and Zn²⁺ were monitored using differential pulse polarography (DPP). During the time of pre-corrosion varying from 0 to 6 d, an "induction period" of the corrosion occurs in the first one - 2 h when no Fe²⁺ ion is released in the solution. After this period, Fe²⁺ was identified in solution and its concentration progressively increases up to 6 h, then starts to decrease and after 6 d nearly disappears. Experiments with Zn²⁺ reveal that the most efficient Fe⁰ remediation occurs after 6 h of pre-corrosion. This coherence thus proves that the presence, the amount and the age of FeCPs ("degree" of corrosion) significantly impact the removal efficiency of Zn²⁺ in Fe⁰/H₂O systems. The present study severely refute the wording 'reactivity loss' and states that progress in designing sustainable Fe⁰/H₂O systems will not be achieved before the role of "active" FeCPs is clarified.